The present invention relates to a fuel cap which is installed to a filler neck of a fuel tank for automobiles and adjusts pressure in the fuel tank by flowing fluid such as air out of the fuel tank or into the fuel tank from outside when the pressure in the fuel tank is positive or negative.
In the prior art, such fuel cap (hereinafter referred to simply as "cap") is disclosed in an example as shown in FIG. 1 (refer to Japanese Utility Model Laid-open Publication No. Sho 60-179654).
In the cap 11, at normal state, an outer circumferential lip element 13b is biased downward through an annular support plate 14 by a first coil spring (first biasing means) 16 and pressed against an annular projection 12b of a cap body 12, and an inner circumferential lip element 13a is biased upward by a second coil spring (second biasing means) 17 and pressed against a disk-shaped valve plate 18 and closes a fluid flow path 12a of the cap body 12. When pressure in the fuel tank becomes positive pressure of a prescribed valve or more, the outer circumferential lip element 13b is elevated together with the support plate 14 against biasing force of the first coil spring 16 and separated from the annular projection 12b of the cap body 12 so that the positive pressure state within the fuel tank is eliminated through the gap. Also when pressure in the fuel tank becomes negative pressure of a prescribed valve or more, the valve plate 18 is moved downward against the biasing force of the second coil spring 17 and separated from the inner circumferential lip element 13a so that the negative pressure state within the fuel tank is eliminated through the gap. Numeral 10 designates a filler neck.
In the cap 11, however, at normal state, since the fluid flow path 12a of the cap body 12 is closed by the first coil spring 16 biasing the outer circumferential lip element 13b downward and the second coil spring 17 biasing the inner circumferential lip element 13a upward, the two coil springs 16, 17 and the valve plate 18 are indispensable.